Radio network controller (rnc) and method for optimising decision regarding operational states for an umts user equipment (ue)

ABSTRACT

A Wireless communication s stem ( 100, 200 ) Comprises an infrastructure element that allocates wireless resources to one of a plurality of wireless communication units ( 112 - 116 ) dependent upon an operational state of the wireless communication unit. The infrastructure element transitions the wireless communication unit between a plurality of operational states based on a variable, service or quality of service accessed by the wireless communication unit. The transitional, preferably, used in a Radio Resource Controller (RRC) state model, are based on the QoS class of the service that, the communication unit is using. An improvement in signalling load results from reduced signalling procedures required for mobility management, session management and RRC connection management.

FIELD OF THE INVENTION

This invention relates to reducing signalling load in a wireless,communication system. The invention is applicable to, but not limitedto, maintaining a different set of Radio Resource Control (RRC)sub-state switching algorithm parameters for each Quality of Service(QoS) class at a Radio Network Controller (RNC) and engaging theappropriate set of parameters based on the service or QoS class of theservice that a user is currently accessing.

BACKGROUND OF THE INVENTION

Wireless communication systems, for example cellular telephony orprivate mobile radio communication systems, typically provide for radiotelecommunication links to be arranged between a plurality of basetransceiver stations and a plurality of subscriber units.

In a wireless communication system, each base transceiver station hasassociated with it a particular geographical coverage area (or cell). Aparticular communication range defines the coverage area where the basetransceiver station can maintain acceptable communications withsubscriber units operating within its serving cell. Often these cellscombine to produce an extensive coverage area. The cells are typicallygeographically distinct with a coverage area that overlaps withneighbouring cells.

Wireless communication systems are distinguished over fixedcommunication systems, such as the public switched telephone network(PSTN), principally in that mobile stations move between coverage areasserved by different BTS (and/or different service providers) and, indoing so, encounter varying radio propagation environments. Therefore,in a wireless communication system, subscriber units perform handoveroperations, when moving between different geographical areas/cells sothat they can be supported in their communications by the nearest basetransceiver station, which typically offers the highest qualitysignal/communication link.

A fixed network interconnects all base transceiver stations. This fixednetwork comprises communication lines, switches, interfaces to othercommunication networks and various controllers required for operatingthe network. A call from a subscriber unit is routed through the fixednetwork to the destination node or communication unit specific for thiscall. If the call is between two subscriber units of the samecommunication system the call will be routed through the fixed networkto the base transceiver station of the cell in which the othersubscriber unit is currently located. A connection is thus establishedbetween the two serving cells through the fixed network.

Alternatively, if the cell is between a subscriber unit and a telephoneconnected to the Public Switched Telephone Network (PSTN) or a PacketData Network (PDN), such as the Internet, the call is routed from theserving BTS to the interface between the cellular mobile communicationsystem and the PSTN or PDN. It is then routed from the interface to thetelephone by the PSTN or PDN.

The Universal Mobile Telecommunication System (UMTS) Standard hasdefined a Radio Resource Control (RRC) state transition model, for theassignment of air-interface bandwidth. The standardised RRC model ismaintained at a subscriber unit, termed user equipment (UE) in UMTSparlance, and its Serving Radio Network Controller (SRNC). The RNC isresponsible for initiating transitions between states of the model andis expected to manage these UE operational transitions based on theactivity and mobility of the UE.

The RRC model defines a number of states, with a variety of statetransition opportunities to move between the various states. The statesinclude four connected states (CELL_CDH, CELL_FACH, CELL_PCH andURA_PCH) as well as an idle state. In Cell _DCH (a dedicated channel ina cell), a large amount of radio resource is available and allocated fora user's use. In Cell_FACH (a fast access channel in a cell), the radioresource is shared with a number of other users. In Cell/URA_PCH (apacket data channel in a cell or in a UMTS radio access mode), the usersare not allocated any radio resource per se. However, in this state, itis easy to move to one of the first two states to obtain radio resource.In an ‘idle’ state, the process to acquire radio resource is much morecomplicated, i.e. more involved signalling including slow securityfeatures are required.

With this in mind, the RNC controls the progress of the UE through thesevarious states based on particular vendor specific algorithms. Thealgorithms, and the selection of parameters, used to control the statesand transitions between states are not standardised. However, within theUMTS standard, some transition algorithms are specified to use timers(as described in Technical Specification TS 25 331). Nevertheless, anumber of transition algorithms are undefined as to how they are to beimplemented, such as: Cell_DCH to Cell_FACH, Cell_DCH to Cell_cPCH,Cell_DCH to Cell_uPCH, Cell_FACH to Cell_DCH, Cell_FACH to Cell_cPCH andCell_FACH to Cell_uPCH.

All algorithms tend to be based around how busy a particular user is,i.e. the busier the user, the more likely it is that the user shouldstay at their highest appropriate radio resource allocation. If a UEremains non-transmitting/non-receiving for a long period of time, thenetwork slowly moves the UE down the state chain. Each activity willcontribute to an algorithm.

In practice, in order to identify a period of time of a user'sactivity/inactivity in one or more of the states, timers are generallyused. Thus, when a pre-determined time period for any state has elapsed,a user may transition to another state under control of its SRNC.

To highlight a practical example of the above operation, let us considerthe following. As is known, the RRC state model in the RNC is engagedwhenever a user establishes a signalling connection to the RNC. Theactivity of the UE in the user plane dictates the transitions betweenthe various states in the RRC model

A user actively transmitting user plane data is identified as operatingin, for example, either a Cell FACH or a CellL_DCH state, depending onthe type of radio bearers that have been established.

Let us assume, for example, that a user is in a Cell-FACH state. If theuser remains inactive for a period of time that is long enough to causethe Cell-FACH timer to expire, the RNC signals the UR to move to aCell-PCH state. If the period of inactivity is further extended, the UEmay be subsequently instructed to a URA-PCH state and then ultimately toan RRC-Idle state at which time the RRC connection is released.

When the UE resumes activity on the bearer plane, different signallingprocedures are required depending on the sub-state in which the UE iscurrently residing. If the bearer activity is mobile-terminated, i.e.another source initiates the connection, the UE has to be paged. Thenumber of cells to which the paging messages are sent depends on thesub-state of the UE. Moreover, the number of mobility updates sent bythe UE is also sub-state dependent.

Thus, the more inactive the UE, the more signalling is required tochange a UE's state to an active state. As the UE moves from Cell-FACHdown to RRC-Idle, the number of mobility updates is reduced whereas thepaging load increases. Therefore, management of the transitions betweenRRC sub-states has a direct impact on management of the signalling loadin the network.

The inventors of the present invention have recognised and appreciatedthat a known technique of solely using timers with a single fixedthreshold in an RRC model to control the operation and allocation ofradio resources using RRC states and transitions, is unnecessarilylimiting and unrepresentative of the needs of users and the Operators.As the algorithm driving transitions between the sub-states is based onbearer activity (activity on the user plane), a single set of timervalues cannot be optimal for all service. Thus, the known technique ofdefining a single set of timers and timer thresholds may providemanagement of resources and signalling for one service, but willundoubtedly lead to less than optimal resources being provided to theuser when accessing another service.

Thus, there exists a need in the field of the present invention toprovide a communication system and a method for reducing signalling loadby better management RRC states and transitions, wherein theaforementioned disadvantages may be alleviated.

STATEMENT OF INVENTION

In accordance with a first aspect of the present invention there isprovided an infrastructure element, as claimed in claim 1.

In accordance with a second aspect of the present invention, there isprovided a communication system, as claimed in claim 9.

In accordance with a third aspect of the present invention, there isprovided a method of reducing signalling load in a wirelesscommunication system, as claimed in claim 11.

In accordance with a fourth aspect of the present invention there isprovided a wireless communication system, as claimed in claim 12.

In accordance with a fifth aspect of the present invention there isprovided a wireless communication unit, as claimed in claim 13.

In accordance with a sixth aspect of the present invention there isprovided a storage medium, as claimed in claim 14.

In summary, the inventive concepts of the present invention alleviatethe problems associated with prior art mechanisms by assigning a varietyof different algorithm parameters, such as timing parameters, in theallocation of resources using the RRC model. In particular, thepreferred embodiment of the present invention proposes to define and useoptimal algorithm parameters or sets of parameters for each valid userservice and/or Quality of Service (QoS). Furthermore, the inventiveconcepts of the present invention proposes transitioning between thestates as the user's traffic profile changes, i.e. the user changes theservice or quality of service that they are accessing.

Hence, by allocating resources in the RRC model, based on a trafficprofile such as a service and/or quality of service, the consequenteffects on the signalling levels can be controlled. In this manner, theinventors have proposed a mechanism to address the scenario wheredifferent QoS classes experience different traffic profiles, such asdata packet activity, usage rates, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will now be described,with reference to the accompanying drawings, in which:

FIG. 1 shows a block diagram of a (UMTS) cellular radio communicationssystem adapted to support the various inventive concepts of anembodiment of the present invention;

FIG. 2 shows a state transition diagram adapted to support the variousinventive concepts of an embodiment of the present invention; and

FIG. 3 illustrates a flowchart for reducing signalling load in awireless communication system, in accordance with embodiments of thepresent invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1, a cellular-based communication system 100 isshown in outline, in accordance with an embodiment of the invention. Inthe embodiment of the invention, the cellular-based communication system100 is compliant with, and contains network elements capable ofoperating over, a UMTS air-interface. In particular, the inventionrelates to the Third Generation Partnership Project (3GPP) specificationfor wide-band code-division multiple-access (WCDMA) standard relating tothe UTRAN radio Interface (described in the 3G TS 25.xxx-series ofspecifications) and is described with reference to such a communicationsystem. However, it will be apparent to a skilled person that thepresent invention is not limited to a UMTS communication system.

A plurality of subscriber terminals (or user equipment (UE) in UMTSnomenclature) 112, 114, 116 communicates over radio links 118, 119, 120with a plurality of base transceiver stations, referred to under UMTSterminology as Node-Bs, 122, 124, 126, 128, 130, 132. The systemcomprises many other than UEs and Node Bs, which for clarity purposesare not shown.

The wireless communication system, sometimes referred to as a NetworkOperator's Network Domain, is connected to an external network 134, forexample the Internet. The Network Operator's Network Domain includes:

-   -   (i) A core network, namely at least one Gateway General packet        radio system (GPRS) Support Node (GGSN) 144 and/or at least one        Serving GPRS Support Node (SGSN) and    -   (ii) An access network, namely one or more UMTS Radio network        controllers (RNC) 136-140 and a number of associated UMTS Node        Bs 122-132.

The GGSN 144, 145 and SGSN 142, 143 are responsible for GPRS or UMTSinterfacing with a Packet Data Network (PDN) such as the Internet 134 ora Public Switched Telephone Network (PSTN) 134. A SGSN 142, 143 performsa routing and tunnelling function for traffic within say, a GRPS corenetwork, whilst a GGSN 144, 145 links to external packet networks, inthis case ones accessing the GPRS mode of the system.

The Node-Bs 122-132 are connected to these external networks, throughbase station controllers, referred to under UMTS terminology as RadioNetwork Controllers stations (RNC), including the RNCs 136, 138, 140(with only three RNC being shown for clarity purposes only), and SGSN142, 143 (with two SGSN being shown for clarity purposes only).

Each Node-B 122-132 contains one or more transceiver units andcommunicates with the rest of the cell-based system infrastructure viaan I_(ub) interface, as defined in the UMTS specification.

Each RNC 136-140 may control radio resources for one or more Node-Bs122-132. The Operations and Management Centre (OMC) 146 is operablyconnected to RNCs 136-140 and Node-Bs 122-132. The OMC 146 administersand manages sections of the cellular telephone communication system 100,as is understood by those skilled in the art.

In accordance with an embodiment of the invention, one or more RNCs136-140 has been adapted, to offer, and provide for, improved radioresource control (RRC) of a plurality of UEs. The adapted operation andinter-working of the RNC is preferably implemented in software, forexample in a digital signal processor 148, 150 contained in the RNC, butmay alternatively be implemented using an additional processor or othermeans as will be apparent to a skilled person, and all such variationsare intended to be included in the present invention. The adapted RNC,say RNC 163, is further described with respect to FIG. 2 and FIG. 3.

The RNC has been adapted to maintain a set of algorithm parametervalues, such as timer thresholds, for each QoS class or service accessedby a UE user. In this regard when the radio resources, termed radiobearers (RABs), and RRC connections are first established (orrenegotiated), the QoS class in the establishment message(s) preferablydictates those timer threshold values to use at the RNC to drive thetransitions between RRC states. By selecting various timer thresholdvalues according to the UE traffic profile for each QoS class (orservice), optimal timer threshold values can be selected. This providesa suitable trade-off between mobility-related and bearer-relatedsignalling traffic.

Although the preferred embodiment of the present invention is describedwith reference to an RNC providing radio resource control based on a setof timers and/or timer thresholds associated with varying QoS or classesof services, it is envisaged that the inventive concepts hereindescribed can be applied to any RRC algorithm parameter. Hence, theinventive concepts are not considered as being limited to timers and/ortimer thresholds.

It is also within the contemplation of the invention that alternativeradio or cellular communication architecture, such as private or publicmobile radio communication systems or other wireless communicationsystems could benefit from the inventive concepts described herein.

More generally, the dynamic adaptation of RNC 136, re-programmedaccording to the preferred embodiment of the present invention, may beimplemented in any suitable manner. For example, new apparatus may beadded to a conventional RNC, or alternatively existing parts of aconventional RNC may be adapted, for example by re-programming one ormore processors therein. As such the required adaptation may beimplemented in the form of processor-implementable instructions storedon a storage medium, such as a floppy disk, hard disk, programmable readonly memory (PROM); random access memory (RAM) or any combination ofthese or other storage media.

A UE has two state properties—an RRC state and a packet mobilitymanagement (PMM) state. The RRC state is stored at both the UE 112 andthe RNC 136. The PMM state is known at the SGSN 142 and UE 112. Hencethe interaction between these states dictates a granularity of knowledgeof the location of the UE 112 by both the RNC 136 and SGSN 142. Toswitch between states (either PMM and/or RRC), various signalling flowsare required. For example, the signalling flows may be dependent uponone or more of the following:

-   -   (i) On user activity;    -   (ii) On user mobility; and    -   (iii) On timer or timer threshold values.

Referring now to FIG. 2, an RRC state model 200 in the RNC is shown.Initially, before a UE is switched on, the UE is in an RRC-Idle/PMMdetached state 205. In this combination of states, the network does notknow anything about the location of the UR. To move from this statecombination, the UE must perform a PS Attach procedure 210, i.e.switching on and connecting to the network. This procedure establishesan RRC connection to the RNC and an Iu signalling connection to theSGSN. At the end of this procedure, the UE is placed in a Cell-FACH RRCstate/PPM-connected state 220. In this state combination, the locationof the UE is known at the cell level.

When a UE then moves cells, a cell update procedure is required, whichinforms the RNC of the cell the UF is now located in. The SGSN is notinformed of this change, as it only needs to know which RNC the UEchanges, then an SRNC relocation procedure is required, which informsthe SGSN of the new SRNC's identity.

In accordance with the preferred embodiment of the present invention,once a UE attaches to an SGSN after first establishing a signallingconnection to the RNC, a plurality of timers and associated timerthreshold levels 201 are activated. The plurality of timers andassociated timer thresholds 201 determine subsequent state changes forthe duration of the attach period. Notably, the respective timerthreshold values are variable, with the levels based on a UR's serviceor quality of service, as known by its SRNC.

This is also the case after a UE has activated a packet data protocol(PDP) context. When a mobile activates a PDP context, the QoS class ofthe service is used to dictate whether the bearers are set up on arandom access channel (RACH)/FACH (moving the UE to CELL_FACH) or DCH(moving the UE to CELL_DCH). Subsequently, the activity of the userdetermines the RRC state of the user.

A transport channel switching algorithm is used to determine theparameters used in switching between Cell_FACH and Cell_DCCH, forexample, dependent upon the transport channel a UE is operating on andin response to the nature of the traffic on that channel. The knownswitching algorithm monitors a UR's continuing activity of use of a DCHchannel to maximise its efficiency. A DCH is suited to continuous use,for example, video/audio and other data streaming, high bandwidthservices that require a small delay. In contrast, a FACH is more suitedto bursty packet-based services, as it is a shared resource, i.e. manyusers using this one channel with bursty traffic makes it appear acontinuously used channel.

If the UE is in a Cell-FACH state, a first timer T_Cell_FACH—isconfigured to expire after a first period of time (exceeding a firsttimer threshold 202) 225. If the UE has been inactive for this period,it is then moved into Cell-PCH state 230. While the UE is in a Cell-PCHstate 230, it performs a Cell Update procedure 235 every time it crossesa cell boundary. If there is any incoming traffic from the network, itis paged only in one cell, as the UE is known to be in that cell.

In accordance with the preferred embodiment of the present invention,when in the Cell-PCH state 230, a second timer T_Cell_PCH is running.Once the second timer expires 240 by exceeding a respective second timethreshold 203, the next mobility flow that the UE executes, i.e., a cellupdate 235, places the UE in a UMTS Radio Access Network (UTRAN)Registration Area (URA)-PCH RRC state 245. A URA is a collection ofcells, which may overlap with neighbouring URAs. In a URA-PCH state 245,a location of the UE is identified by the identity of the URA containingthe UE. The mobility procedure URA Update is performed when the UEchanges its URA identity before the UE is able to receive traffic, itmust first be paged in each cell within that URA. Once the UR's cell hasbeen identified, the connection can be established and the trafficdelivered.

In URA-PCH state 245, a third timer T_URA_PCH is running. Once the thirdtimer expires 250 by exceeding a third timer threshold 204, the UE mustrelease all resources and move to an RRC-Idle/PMM-Idle state 275. Thetransition to an RRC-Idle/PMM-Idle state 275 is performed by the RNC,which initiates a RRC Connection Release and Iu Signalling Releaseoperation 280.

When these transitions are complete, the location of the UE is known bythe Routeing Area identity. A routeing area consists of a number ofcells and typically covers a number of URAs. In this state, the UE isrelatively inactive and only performs a mobility (Routing Area) updatewhen it crosses routing area boundaries. However, incoming traffic fromthe network now requires that the UE is paged in every cell within therouting area.

In this instance, setting incorrect algorithm parameter values (such astimer thresholds) for a particular service would have a major impact onthe air interface throughout, as UEs in a Cell_CDH state 260 occupy muchmore resource than those in a Cell_FACH state 220. However,transitioning a UE between a Cell_DCH state 260 and a Cell_FACH state220, thereby lowering its activity status at its SRNC, incurs asignalling overhead.

Timer and timer threshold values also dictate other RRC statetransitions. The main timer-initiated state transitions are:

-   -   (i) Cell_FACH to Cell_PCH 225;    -   (ii) Cell_PCH to URA_PCH 235, 240; and

-   (iii) URA_PCH to RRC_Idle 245, 275.

The duration spent by a UE in each of these states is essentially (in anover-simplistic view) dictated by the time between sending packets.

Hence, the duration spent in each state has a large effect on the levelsof mobility and paging signalling in the network. This can be explainedby the following. If a UE is in idle mode, the UE performs the leastnumber of mobility flows. However, because of this, the network fails tohave a good indication of the location of the US. Consequently, thenetwork needs to page a large number of cells to try and locate the UE,when a call for that UE is received. Conversely, if a UE is in any ofthe Cell_xxx states, the network knows precisely the location of the UEdue to many more mobility signalling flows at the UE movies within thenetwork. Hence, there is no need to page a number of cells whenreceiving a call for the UE.

In summary, in Cell_FACH and Cell_PCH states, the network knows thelocation of the UE at the cell level. In a URA_PCH state, the locationof the UE is known at the URA level, and when the UE is in an idle statethe location of the UE is known at the routing area level. In thisrespect, the further the UE is towards operating in an idle state, theless mobility signalling is performed. The inventors of the presentinvention therefore propose shorter timer thresholds to minimise thesignalling traffic for mobility.

On the other hand, if the UE receives subsequent traffic when not in aCell_FACH or a Cell_DCH state, the UE must first be paged. The UE ispaged at a granularity that its location is known at, as indicatedabove. Thus, a UE in an idle state is paged in more cells than a UE in aURA_PCH state, which would, in turn, also be paged in more cells than aUE in Cell_PCH state. In this respect, the inventors of the presentinvention propose to use longer timer threshold values in order tominimise paging traffic levels. Also, if the mobile is in an idle state,RRC and Iu signalling connections have to first be restored, incurringextra signalling traffic and delays in setting up the required bearers.

It is known in the UMTS arena that each service has a specific trafficmodel, which determines the length of periods of activity andinactivity. Services in UMTS are already grouped according to their QoSclass. Therefore, in the preferred embodiment of the present invention,a set of timer threshold values is allocated for each UMTS QoS classgroup.

The example below illustrates the difference, and therafter a preferredimplementation, between two services belonging to two different QoSclasses.

Let us consider two services such as email and Web access/downloads. Anemail service belongs to a ‘background’ QoS class, whereas a Web servicebelongs to the ‘interactive’ QoS class. A typical email download ofabout one Kbyte in size is expected to last for about five seconds.Therefore, it is proposed that in the case of services such as email,timer threshold values are set to be relatively short, in order to allowresources to be released as soon as the download is complete.

Similarly, for example, a short message service (SMS) sessio with onemessage may be of the order of one hundred bytes long with a meaninter-session time of say, sixteen hours. SMS would typically bedescribed as long periods of inactivity between about “conversation”where the active periods are of the order of single packet up/downloads.In a similar manner to an email service, it is proposed that timerthreshold values are set to be relatively short, in order to swiftlymove the UE into an idle state, thereby freeing up resources in thenetwork.

With a user activity/traffic profile that entails a significant amountof web browsing, a different timer threshold should be used. In webbrowsing, a short packet is sent to the network from the UE (e.g. a HTTP‘Get’ request). In response to the UE's request, a relatively largeamount of data is sent to the UE. A period of silence (i.e. user ‘read’time) would follow at both ends of the link, before the UE would send afurther ‘Get’ request. A web session may consist of a download ofseveral files of, say, fifteen Kbytes each, separated by a reading timeof about one minute, i.e. an average of five web pages are read. Websessions, for example, may have a mean inter-session time ofapproximately two and a half hours, with a mean session length up to,say, five minutes.

Therefore, in contrast to SMS or email type services, it is proposedthat in the case of services such as a web service, timer thresholdvalues are set to be relatively long. In this manner, a longer timerthreshold reduces the possibility of a timer expiring during aweb-reading time, thereby avoiding the necessity to re-establishresources every time a new web page is to be downloaded.

This would be in contrast to a third user activity profile entailing asignificant level of accessing Streaming services. This profile would bedescribed by long periods of a user downloading and/or uploading largeamounts of data. Hence, algorithm parameter thresholds that areidentified as being suitable for one service may be deemed unsuitablefor others within timer function 201.

It is envisaged that any other QoS classes or services may be used toinfluence the timer threshold values in an RNC's RRC model. In thiscontext, the QoS classes may include, but are not limited to:Background, Conversational, Streaming, and Interactive. Furthermore,each UMTS UE is mapped into a QoS class depending upon the bit-raterequired and the delay requirements. Therefore, the preferred embodimentof the present invention, as illustrated in FIG. 2, comprises multiplesets of timers and respective threshold values, dependent upon therespective QoS classes and or services of the traffic.

The RNC is configured to trigger the correct set of timer thresholdvalues dependent upon the QoS class of the service that a user isaccessing. Preferably, in a UMTS context, the RNC uses the establishmentcause of the RRC connection set up mechanism to determine which set oftimer threshold values to use for a given service.

In an alternative embodiment, the RNC uses radio bearer (RAB) parametersprovided in a RANAP RAB Assignment Request to determine those set oftimer threshold values to use for a given service. The radio accessnetwork access protocol (RANAP) is the controlling protocol between thecore network (SGSN and MSC) and the RNC. When a radio access bearer(RAB) is set up via a RANAP (and UTRAN signalling) connection, a UEobtains both radio resource and core network resource. Notably, the RNCknows a UE's QoS class, but not necessarily the service accessed by theUE. Therefore, it is also proposed that the respective traffic modelsare also evaluated for the services within a QoS class.

Referring now to FIG. 3, a flowchart 300 indicating a preferred timerthreshold optimisation mechanism is illustrated. The process commencesin step 305 where a ‘cost’ function for a particular service or QoS isquantified for a particular algorithm parameter value (such as a timerthreshold). Once the cost function is quantified in step 305, thepreferred process follows one of two routes to identify optimum value tobe used, as illustrated in step 308. Whichever route is selected, theprocess is applied to each QoS class to obtain the best possiblealgorithm parameter (timer threshold) values for each QoS class. Askilled artisan would recognise that alternative routes could be usedfor the UMTS and other communication systems.

A first route starts at any one or more arbitrary, but reasonable,value(s) of the algorithm parameter, as shown in step 310. The firstroute then perturbs these one or more values gradually, in step 315, todetermine whether the overall cost function changes. It is proposed thatthe first route is typically applied when the underlying system isdifficult to define in mathematical terms, i.e. it would fall into a‘Numerical Techniques for Optimisation’ category.

This first method requires running multiple consecutive simulations toevaluate the cost function associated with particular algorithmparameters, such as timer threshold values, as shown in step 320. Thesealgorithm parameter values are then changed dynamically and in anintelligent manner to gradually reduce the total cost function in step325.

A second route may be used if a complete mathematical description of thesystem is, or can be generated, and is readily manipulated, in step 340.In this regard, a cost function may be defined in terms of theparameters of the system. The cost function equation derivative is thenset equal to zero, as shown in step 345. The cost function equationderivative is solved for the various algorithm parameter values (such astimer threshold values) to yield a set of optimum values, as shown instep 350. This second route may be referred to as the ‘AnalyticalSolution’, as it requires an extensive use of algebra and statistics,and may result in multiple possible solutions.

Also, for either route, the process is repeated over time in step 355,to address changes in the UE's service usage profile changes over time.For example, it is known that the usage of a mobile telephone and itsfeatures by a user increases as it becomes a more essential part of theuser's everyday life. With this in mind, a periodic intermittent orcontinuous re-evaluation of the parameter values is implemented.

It is envisaged that a suitable cost function could be of the form:J=k ₁(s _(p) q _(p))² +k ₂(s _(m) q _(m))² +k ₃(d _(a) q _(a))²  [1]

Where:

-   -   J is the overall cost value;    -   K₁, k₂, k₃ are user definable constants;    -   S_(p) is the typical paging message size;    -   Q_(p) is the quantity of paging messages transmitted;    -   S_(m) is the typical size of mobility messages;    -   Q_(m) is the quantity of mobility messages transmitted;    -   D_(a) is the typical delay due to activity in the incorrect        state; and    -   Q_(a) is the quantity of these occurrences.

Notably, each of the terms in the cost function is a squared value toease the differentiation calculation, as well as guaranteeing a positivecost function. If the cost function is quadratic in nature, then anystationary points on the curve are at least local minima identifyingoptimal values.

The complexity involved in defining the variables in the cost functionis, in the preferred embodiment, dependent upon the timer thresholdvalues and the UE traffic profile. For a full analytical solution to beperformed, the different services in a QoS class should be profiled asstatistical distributions and combined into the cost function. Solutionswould then also be dependent upon the tolerances one wishes to place onthe solution.

Although the above scenarios are all described with reference tomanagement of transitions between the RRC states in the RRC state model,it is within the contemplation of the invention that the inventiveconcepts can be applied to any state-based model of a communicationunit's operation. Furthermore, although the inventive conceps have beendescribed with reference to an RNC in a UMTS system, it is within thecontemplation of the invention that the inventive concepts can beapplied to any suitable element/function in any type of communicationsystem.

It will be understood that the communication system, communication unit,and method for reducing signalling load in a wireless communicationsystem described above tends to provide at least one or more of thefollowing advantages:

-   -   (i) A more effective management of resources and signalling        load. This results from transitions in the RRC state model being        based on the QoS class of the service that the US is using.    -   (ii) An improvement in signalling load results from reduced        signalling procedures required for mobility management, session        management and RRC connection management.    -   (iii) It also potentially improves the end user experience, as        less time may be spent establishing radio resource due to        efficiency gains in accessing services.

Whilst specific, and preferred, implementation of the present inventionare described above, it is clear that one skilled in the art couldreadily apply variations and modifications of such inventive concepts.

Thus, a communication system, and a method for reducing signalling loadhave been provided wherein the aforementioned disadvantages associatedwith prior art arrangements have been substantially alleviated.

1. An infrastructure element in a wireless communication system, theinfrastructure element comprising means for employing a radio resourcecontrol state model to determine transition(s) of a wirelesscommunication unit between a plurality of operational states means forallocating wireless communication resources to said wirelesscommunication unit of a plurality of wireless communication unitsdependent upon an operational state of said wireless communication unit,means for transitioning said wireless communication unit between theplurality of operational states based on a variable traffic profile ofsaid wireless communication unit.
 2. The infrastructure elementaccording to claim 1, wherein said traffic profile is a service orquality of service accessed by said wireless communication unit.
 3. Theinfrastructure element according to claim 1, wherein said wirelesscommunication system is a universal mobile telecommunication system andsaid infrastructure element is a radio network controller.
 4. Theinfrastructure element according to claim 3, wherein said transition(s)between said plurality of operational states is based on one of a set ofalgorithm parameters, such that a different set of algorithm parametersis used for substantially each respective quality of service class. 5.The infrastructure element according to claim 3, wherein saidtransition(s) between said plurality of operational states is based onone of a set of timers, such that a different timer is used forsubstantially each respective quality of service class.
 6. Theinfrastructure element according to claim 5, wherein said set of timerscomprises a set of thresholds for each respective quality of serviceclass such that a different timer threshold is used for substantiallyeach respective quality of service class.
 7. The infrastructure elementaccording to claim 6, wherein timer threshold levels are based on alength of time a wireless communication unit accesses a service orquality of service.
 8. The infrastructure element according to claim 3,wherein said radio network controller uses an establishment cause of oneof the group of said radio resource control set up mechanism or radioaccess bearer parameters in a RANAP radio access bearer assignmentrequest to determine which service is used by the wireless communicationunit. 9-10. (canceled)
 11. A method of reducing signalling load in awireless communication system comprising an infrastructure element thatallocates wireless resources to one of said plurality of wirelesscommunication units dependent upon an operational state of a wirelesscommunication unit, the method comprising the steps of: quantifying acost function for a particular service or quality of service accessed bysaid wireless communication unit in order to transition between wirelesscommunication unit operational states; the method characterised by thesteps of: evaluating a cost function derivative to identify an algorithmparameter, wherein said cost function is dependent upon a variabletraffic profile of a service or quality of service accessed by saidwireless communication unit; and transitioning said wirelesscommunication unit between a plurality of operational states based onsaid evaluation.
 12. The method of reducing signalling load in awireless communication system according to claim 11, wherein said stepof evaluating comprises evaluating one of a set of algorithm parameters,such that a different set of algorithm parameters is used forsubstantially each respective traffic profile. 13-16. (canceled)